**Core Concept**
A fixed oxygen delivery device refers to a medical device that delivers a fixed concentration of oxygen to a patient, regardless of their respiratory rate or effort. These devices are commonly used in critical care settings to provide a consistent and controlled level of oxygen therapy.

**Why the Correct Answer is Right**
The correct answer is a device that uses a nasal cannula or mask to deliver a fixed concentration of oxygen, typically between 24% to 60%. This type of device is designed to provide a consistent flow of oxygen to the patient, regardless of their respiratory rate or effort. The oxygen flow rate is usually set by the healthcare provider and is not adjusted based on the patient's respiratory status.

**Why Each Wrong Option is Incorrect**
**Option A:** A variable oxygen delivery device, such as a Venturi mask, is incorrect because it delivers a variable concentration of oxygen based on the oxygen flow rate and the size of the venturi valve.
**Option B:** A non-rebreather mask is incorrect because it delivers 100% oxygen, but the flow rate can vary based on the patient's respiratory rate and effort.
**Option C:** An oxygen tent is incorrect because it delivers a high concentration of oxygen, but the flow rate and concentration can vary based on the patient's respiratory status.

**Clinical Pearl / High-Yield Fact**
One important thing to remember is that fixed oxygen delivery devices should be used with caution in patients with respiratory failure or those who require high concentrations of oxygen, as they may not provide sufficient oxygen to meet the patient's needs.

**Correct Answer: D. Non-rebreather mask is incorrect because it delivers 100% oxygen. The correct answer is a fixed oxygen delivery device that delivers a fixed concentration of oxygen, which is typically a nasal cannula or mask.